The placenta is an active endocrine organ producing large amounts of steroid and peptide hormones during human gestation. Among the peptides that the placenta produces some are similar in structure to hypothalamic and pituitary hormones and have an important physiologic role in the mother and fetus during pregnancy. Corticotropin releasing hormone (CRH) is a neuropeptide produced in the hypothalamus which regulates pituitary and adrenal function. CRH peptide and mRNA have been identified in extracts of human placenta and this hypothalamic-like placental hormone has now been studied extensively in human pregnancy. The overall objective of these studies is to determine the cellular distribution of corticotropin releasing hormone in the human placenta and to investigate mechanisms that might regulate placental CRH synthesis in relation to gestational age and parturition. The sites of CRH synthesis and/or storage will be investigated throughout the first, second, and third trimesters of pregnancy. Sites of CRH gene expression determined by in situ hybridization will also be investigated. Based on prior clinical data, we hypothesize that of CRH mRNA and peptide are stimulated in placentas following the onset of preterm labor. Studies will be conducted to investigate this hypothesis as well as to examine the regulation of placental CRH production of glucocorticoids, estradiol and progesterone. The results of these studies will reveal important information about the possible role of placental CRH in mechanisms of parturition and its regulation in human pregnancy.